The PQ has consistently tried to claim the ethical high ground in the campaign leading to Monday's election, pointing to alleged scandals during ex-Liberal premier Jean Charest's three terms in power between 2003 and 2012.

It has also angered Liberal Leader Philippe Couillard by trying to draw links between him and Arthur Porter, a former hospital administrator and ex-federal spy watchdog who is now charged with fraud.

On Tuesday, however, it was Marois who was being dogged by questions about ethics as she reacted once again to a report by the CBC's French-language network that husband Claude Blanchet asked an engineering company executive for $25,000 in 2007.

The money was allegedly destined for Marois's run at the PQ leadership -- a race that never took place because she was eventually acclaimed leader.

The engineering executive made the allegations in a sworn affidavit but Radio-Canada did not release his name at his request.

Testimony at the Charbonneau Commission into construction-industry corruption has indicated that engineering firms have been generous contributors to political parties.

For example, it was revealed that Dessau gave a total of $1 million to the two major parties between 1996 and 2011 -- $600,000 to the Liberals and $400,000 to the PQ.

Marois questioned the timing of the executive's soul-bearing, considering it surfaced in the last week of the campaign.

"Why did he do this now if he knew the situation in the past," she said in Drummondville.

"Why did he decide to denounce this situation now? Because we are in an election and he doesn't want the return of a Parti Quebecois government."

She said some people fear the re-election of the PQ because "we are the best way to fight against collusion and corruption."

Couillard said the allegations raise questions about the PQ's integrity.

"I'm not presuming guilt," the Liberal leader said while campaigning in Montreal. "I'm just noting the discrepancy between what we're hearing and the supposed declarations of purity by the Parti Quebecois in the last two or three years."

Even though Blanchet denied the allegations in the Radio-Canada report, Couillard said questions still need answered. He also rejected Marois's arguments that the revelation was an act of revenge.

"I think the facts speak for themselves," he said, adding voters will draw their own conclusions.

Couillard also pointed out that all parties have had their reputations tarnished over political financing in the last decade and that new rules have helped improve the situation.

In the affidavit cited by Radio-Canada, the executive says he gave Blanchet $25,000 in the form of various cheques up to $3,000, which at the time was the maximum individual contribution allowed in the PQ leadership race.

The affidavit states the man's company gave him the cheques and that he in turn handed them over in an envelope to Blanchet because he "wanted to have special access to Madame Marois."

Marois insisted she, her husband and the PQ have always respected the law on the party financing.

Radio-Canada said the man told the French-language network of the CBC he has known Blanchet for 15 years.

It also said Blanchet asked another engineering executive for money ahead of the 2008 provincial election.

The man said he gave Blanchet cheques totalling $5,000 from employees of his firm.

While Coalition Leader Francois Legault called the various allegations "very serious," he said he is ready to accept Marois's and Blanchet's denials at face value.

Marois said Tuesday she has no problem with the matter being examined by the appropriate officials.

"I have no problem with the chief electoral officer giving his point of view on this matter because he never spoke to myself or my party about PQ campaign financing," she said.

But she won't ask him to get involved.

"The chief electoral officer, the auditor general, the ethics commissioner, all these people are independent and it is very important to preserve that independence."

Ethics weren't the only issue to electrify the election campaign on Tuesday. Couillard and Legault tried to jolt their electoral chances by criticizing a 4.3 per cent increase in Hydro-Quebec rates that came into effect on April 1.

Couillard said increases should be indexed to inflation and that his government would push the Crown-owned utility to make further administrative cutbacks.

Legault, who also favours indexation, said flatly that a Coalition government would roll back the hikes to the level of inflation.

"We have to understand that most of the workers, they don't have an increase of 4.3 per cent," he said. "Old people having pensions, they don't have an increase of 4.3 per cent so it's not fair. . . . I think it's unacceptable."

Also on Tuesday, the province's chief returning officer reported an increase in the number of people turning out for advance polls.

Jacques Drouin said in a statement that 1,057,706 people cast ballots last Friday and Saturday, for a turnout rate of 17.68 per cent of registered voters. In the 2012 election, 919,120 people -- or 15.57 per cent -- voted early.

In other campaign news, militant student group ASSE, which is planning a demonstration against the government's austerity budget, predicted that 42,000 students will boycott classes when a massive march is held this Thursday.